Langmuir and Langmuir-Blodgett monolayers of molecular tweezers and clips.

Molecular clips and tweezers are able to selectively bind electron-deficient aromatic and aliphatic substrates. By means of pressure−area isotherms and Brewster angle microscopy (BAM), the self-association process and phase behavior of dimethylene-bridged molecular clips and tetramethylene-bridged molecular tweezers each substituted with two acetoxy groups as polar head groups were investigated. In a series of experiments, we observed that the molecular surface area of the clips and tweezers only depended on the skeletal structure and not on the polar groups. The measured areas agreed with the effective molecular diameters of the molecules if the aromatic side walls of the clips or tweezers were assumed to be aligned perpendicularly to the water surface. We compared the phase behavior of the pure molecular clips and tweezers with that of the host−guest complexes of these molecules, which were formed with 1,2,4,5-tetracyanobenzene (TCNB) as the guest molecule. For the clips with a central benzene (I) and n...